The present invention relates to a method and device for detecting dirt on eggs, comprising exposing said eggs to ultraviolet light. In particular the invention concerns a method and a device for selecting and sorting eggs upon which dirt is detected
In the field of industrial activity of egg processing it is well known to examine eggs and subsequently to select eggs on certain characteristics for which well-defined criteria are set. The characteristics are mainly weight and crack condition.
In present times of very large and still growing egg processing plants standards on hygienic in treatment of food products are becoming more stringent, for example in regard to dirt on eggs. Remnants of dirt, in particular remnants of albumen and yolk, and also traces of excrements, can cause unwanted infections and consequently can be very disadvantageous during and after processing of eggs. Before removing dirt on eggs, or even to remove dirty eggs as well, it is necessary to detect the dirt adequately and to incorporate this detection in egg sorting procedures.
Historically, see for example the German patent DE 937956, eggs are inspected, more in particular xe2x80x9ccandledxe2x80x9d, before the eggs are sorted. During conveying by a sorting machine, the eggs are exposed to white light from below, mainly in order to make blood spots or cracks visible. Then eggs can be either labeled or removed by hand. In case of sorting such labels are taken into account.
From U.S. Pat. No. 4,622,469 it is known to detect remnants of rotten albumen by exposing eggs to ultraviolet light. The rotten albumen may, for example, originate from broken eggs. According to this patent, such remnants are fluorescent.
In OSRAM-catalogue, named xe2x80x9cLichtprogramm 97/98xe2x80x9d, page 6.12, high-pressure mercury lamps are disclosed as ultraviolet light sources to be used for recognizing remnants of dirt on fruit, meat, fish, etc. From this reference, it is not clear to what extent contrasts in fluorescent image areas can be distinguished.
From Patent Abstracts of Japan Publication Number 56-145350, a stained part of the eggshell is made to fluorescence thereby providing for dirt detection. A disadvantage of the 56-145350 method is that the sorting and selecting of the eggs is rather inaccurate.
The main object of the present invention is to take measures in order to satisfy the above-mentioned standards and criteria, thereby also remedying the shortcomings of the methods and devices known thus far.
Therefore the present invention involves a method as mentioned above, further comprising,
capturing images of exposed eggs, the images comprising pixels, and
determining within the images surface areas of dirt on the basis that egg shells are clearly fluorescent whereas a dirt surface is not fluorescent by correlating data of contrast and data of position of said pixels.
In the present method, the dirt areas appear dark or black. Determination of dirt areas is therefore made on the basis that the dirt surface is clearly fluorescent and the dirt surfaces are not fluorescent, rather than on the basis that the dirt fluoresces.
It has appeared that for both brown and white eggs, when exposed to ultraviolet light, the egg shells are clearly fluorescent whereas the dirt surface areas are not fluorescent. The resulting differences in fluorescence at different parts of the egg surface allow one to obtain contrast data for article surface areas. Consequently by having such data, such surface parts can be compared with present standards and suitable decisions about further treatment and processing can be taken.
Advantageously the invention can be applied for automatic sorting and selecting procedures for large amounts of articles such as eggs. Differences in such sorting and selecting caused by interpretation or tiredness of operators who sort such articles by hand, can be avoided. Moreover, different settings according to correspondingly different requirements, for example as to brightness, can easily be employed.
Another advantage of the present invention is found in inspection of articles already cleaned. Thus dirt which hardly could be observed using conventional methods can be traced.
In another embodiment of the present invention said articles are positioned upon rollers of a conveyor or a conveyor belt in that said articles are rotating about an axis. Either continuous, intermittent, or pulsing exposure, or even combinations, can be employed advantageously in the set-up of the present invention.
Patent Abstract of Japan, publication number 06129987 discloses a method to excite a damaged part of an oil cell for emission by inactivating the surface of citrus fruits etc. with an ultra violet ray. The light is captured with a camera for picture processing. The reference does not disclose a method on the basis of eggshells clearly being fluorescent rather than a dirt surface area looking black.
EP 0 398 444 discloses a method for detecting dirt etc. on egg shells by scanning the egg with a beam light and subsequent detection of the egg by means of a camera.